Effect Of Cathode Diameter On Intense Relativistic Electron Beam Generation In The Presence Of Prepulse

摘要

Intense gigawatt relativistic electron beam generation studies were carried out in the presence ot prepulse. Electron beams were generated using planar and annular graphite cathodes of various diameters at a fixed 25 mm anode-cathode gap. For the planar cathode, the beam parameters obtained are 340 keV, 24 kA, and 100 ns at a 680 A/cm~2 current density. With an annular cathode, 346 keV, 10 kA, and 100 ns electron beam could be generated at a 3.4 kA/cm~2 current density. The peak electric field in the diode varies from 58 to 138 kV/cm. A bipolar prepulse voltage has been recorded at the diode for both the cathodes. The amplitude of the negative prepulse voltage varies with the Marx generator voltage but the time duration remains same. The positive prepulse voltage varies both in amplitude and time duration with the Marx generator voltage. Some shot to shot variation in the diode voltage and current were recorded for the annular cathode due to the nonreproducibility of the prepulse generated plasma. It was found that the effect of prepulse is more pronounced in the cathode of larger diameter.